Mobile communication systems were developed to provide the subscribers with voice communication services on the move. With the rapid advance of technologies, the mobile communication systems have evolved to support high speed data communication services beyond the early voice-oriented services. However, the limited resource and user requirements for higher speed services in the current mobile communication system spur the evolution to more advanced mobile communication systems.
As one of the next-generation mobile communication systems to meet such requirements, standardization for a Long Term Evolution (LTE) system is underway in the 3rd Generation Partnership Project (3GPP). LTE is a technology designed to provide high speed packet-based communication of up to 100 Mbps and aims at commercial deployment around 2010 timeframe. In order to accomplish the aim, a discussion is being held on several schemes: one scheme for reducing the number of nodes located in a communication path by simplifying a configuration of the network, and another scheme for maximally approximating wireless protocols to wireless channels.
FIG. 1 is a diagram illustrating the general LTE mobile communication system architecture.
Referring to FIG. 1, the radio access network of the LTE mobile communication system includes an evolved Node B (eNB) (hereinafter, referred to as Node B or E-UTRAN interchangeably) 110, a Mobility Management Entity (MME) 120, and a Serving Gateway (S-GW) 130. The User Equipment (UE) 100 connects to an external network through the eNB 110, S-GW 130, and PDN Gateway (P-GW) 160.
The eNB 110 is a Radio Access Network (RAN) node and corresponds to Radio Network Controller (RNC) of Universal Terrestrial Radio Access Network (UTRAN) system and Base Station Controller (BSC) of GSM EDGE Radio Access Network (GERAN) system. The eNB 110 is connected to the UE 100 through radio channel and performs the role similar to the legacy RNC/BSC. The eNB 110 may manage a plurality of cells simultaneously.
In LTE, all the user traffics including the real time service such as Voice over IP (VoIP) are serviced through a shared channel and thus there is a need of a device for gathering the state informations of UEs and scheduling the UEs, eNB being responsible for this.
The MME 120 is an entity responsible for various control functions and may be connected to a plurality of eNBs.
The SGW 130 is an entity responsible for establishing and releasing data bearers under the control of the MME 120.
The Application Function (AF) 140 is an entity responsible for exchanging application information with the UE at the application level.
The Policy Charging and Rules Function (PCRF) 150 is an entity responsible for controlling Quality of Service (QoS) policy and providing the PGW 160 with Policy and Charging Control (PCC) rule. The PCRF 150 is an entity responsible for controlling the QoS and billing for the traffic. Meanwhile, the term “User Plane (UP)” denotes a path established by connecting UE 100, RAN node 110, SGW 130, and PGW 160 for user data transmission. On this path, the link between the UE 100 and the RAN node 110 is established through a radio channel most significantly restricted in terms of resource.
In the radio communication system such as LTE, QoS is applied per EPS bearer. One EPS bearer is used for IP flows requiring the same QoS. For An EPS bearer is configured with QoS-related parameters such as QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). The QCI is a parameter defining QoS priority with an integer value, and the ARP is a parameter for use in determining whether to accept or reject establishment of a new EPS bearer.
The EPS bearer corresponds to the Packet Data Protocol (PDP) context of the GPRS system. An EPS bearer belongs to a PDN connection which may have Access Point Name (APN) as a property. In the case of establishing a PDN connection for IMS service such as Voice over LTE (VoLTE), the PDN connection has to be established using a well-known IMS APN.
In order to support voice communication in the LTE network, it is possible to adopt the IMS-based VoLTE in Packet Switched (PS) mode or the CS Fall Back (CSFB) reusing the Circuit Switched (CS) mode of the 2G/3G system. VoLTE is a term used in LTE network in the same concept as Voice over IMS (VoIMS).
The communication system uses measurement information in order to control handover and transmission/reception power of the UE. The eNB sends the UE the information on the measurement targets and measurement parameters which may include per-measurement target offsets and threshold values for determining measurement report. The UE measures radio parameters of the measurement targets according to the configuration information and reports the measurement result to the eNB when the measurement condition is fulfilled.